This application claims the priority of German Application No. 102004037584.4, filed Aug. 3, 2004, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a drive unit having an electric synchronous machine (particularly, a crankshaft starter generator of a motor vehicle constructed as a synchronous machine), a pulse counter unit for detecting the rotor position during the running operation of the synchronous machine, and a control unit for controlling the synchronous machine.
“Synchronous machines” in the sense of the invention are all electrical machines which, on the basis of their magnetic asymmetry of the rotor, with respect to the stator, have torques generated when the stator winding is excited and, as a result, have a rotational rotor speed synchronous to the stator frequency at least in partial operating ranges. These are in particular: permanent-magnet-excited synchronous motors, electrically excited synchronous motors, reluctance motors, claw pole motors and so-called mixed motors, as well as corresponding generator types which within themselves at least partially combine the above-mentioned motor principles—for example, can assume a mixed form also with the asynchronous machine principle.
In the case of hybrid motor vehicles, synchronous machines of an asynchronous construction (such as short-circuit rotors) and of a synchronous construction are used. In this case, the asynchronous motors are distinguished by the fact that the field of the rotor is impressed by the magnetizing current originating from the stator, and the magnetic orientation of the rotor therefore does not have to be determined by sensors. In the case of synchronous motors, a magnetic asymmetry of the rotor is defined as a result of the construction.
It therefore becomes necessary to know the rotor position of a synchronous motor when the operation of the latter is started. Systems can, for example, be used for this purpose in the case of which the precise rotor position is determined by way of sensor-type absolute-value position generators (such as so-called resolvers or Hall generators with a sine-cosine analysis). However, on the one hand, such sensor systems are very cost-intensive and, on the other hand, require considerable space. Methods are also known which have a so-called sensorless position detection, in which, for identifying the rotor position, the effect of the magnetic asymmetry of the rotor is measured by way of the resulting electrical effect in the stator windings. For identifying the rotor position, both methods require a stationary motor when the operation of the synchronous motor is started. The identification of the rotor position in the case of a stationary rotor is in this case obtained from the applications of industrially used drives, in which the rotor shaft is rigidly connected with the actuators of the application (for example, robot systems).
It is an object of the invention to create a drive unit with a synchronous machine which, by the use of simple devices, ensures a start of the operation of the synchronous machine which is defined at all times.
According to the invention, this object is achieved by providing a drive unit including a synchronous machine, a pulse counter unit for detecting the rotor position during the running operation of the synchronous machine, and a control unit which is constructed such that, with the start of the operation of the synchronous machine, the stator winding of the synchronous machine is energized such that the rotor aligns itself corresponding to a magnetic preference direction parallel to the direction of the magnetic stator field generated by the energizing. In addition, the pulse counter unit is set to a defined starting value.
A defined rotor position is achieved by the targeted energizing of the stator, by which the rotor is caused to align itself corresponding to a magnetic preference direction. In order to be able to determine the rotor position of the synchronous machine in the subsequent operation of the synchronous machine, the pulse counter unit (which shows the angle between the rotor and stator by increments) is set to a defined starting value. In this case, it is a prerequisite that the incremental generator (pulse counter) indicates at least the magnetic periodicity of the electrical synchronous machine. Starting from this defined rotor position, the operation (supply of the stator windings with operating current for generating a magnetic rotating field for the continuous rotor drive) of the synchronous machine can be ensured with a continuously uniform starting behavior. In this case, the magnetic preference direction of the rotor is the direction in which it is aligned such that an energetic minimum is obtained for the superimposition of the stator field and the rotor field. The energizing of the stator windings for the alignment of the rotor preferably takes place by impressing a direct current or a low-frequency current, the frequency and the amplitude being dimensioned such that, despite its inertia and the exterior torques acting upon it, the rotor is reliably capable of following the impressed rotating field on the basis of the frequency.
In the following, the invention will be described for all types of electrical machines based on the example of a synchronous motor. In a particularly preferred embodiment of the invention, the synchronous motor with the pulse counter and the control unit is only a component of a transmission line for a hybrid motor vehicle. The transmission line also includes an internal-combustion engine and a transmission unit, as well as a clutch by which the power transmission between the internal-combustion engine and the transmission can be interrupted. Preferably, two clutches are present. By use of the first clutch, the power transmission between the output shaft of the internal-combustion engine and one end of the drive shaft of the synchronous motor can be interrupted, and, by use of the second clutch, the power transmission between the other end of the drive shaft of the synchronous motor and the input shaft of the transmission unit can be interrupted. The internal-combustion engine, the synchronous machine and the transmission unit are, therefore, arranged in series behind one another in the transmission line and are, in each case, coupled with one another by way of a clutch arranged between two of the components, respectively.
In an alternative embodiment of the transmission line, the synchronous motor with its drive shaft can also be arranged parallel to the input shaft of the transmission unit and, at its input shaft, by way of an intermediate transmission unit with an integrated clutch, can be coupled only with one drive shaft end into the transmission line. In this case, a power-related uncoupling of the synchronous motor can take place only by the controlling of a clutch.
In a contemplated construction, the at least one clutch (depending on the construction—synchronous motor arranged in series or parallel in the transmission line), is controlled by way of the control unit such that the synchronous motor is switched virtually load-free when the operation of the synchronous motor is started. Subsequently, the stator windings of the synchronous motor are energized such that the rotor aligns itself corresponding to a magnetic preference direction. Furthermore, the existing pulse counter unit is set to a defined starting value (for example, starting value=0). Preferably, the setting of the starting value of the pulse counter unit takes place at a point in time at which the rotor of the synchronous motor is already aligned according to its magnetic preference position. Based on this defined starting position, the rotor position determination during the operation of the synchronous motor takes place by the pulse counting of the pulse counter unit.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.